The present invention relates to hydro-pneumatic actuators and particularly to such actuators employed with brake apparatus for railway vehicles. This brake apparatus may be either tread brake units or disc brake units, for example.
Typically, these brake units employ a light spring to maintain constant brake shoe engagement with a wheel or brake disc, in order to generate, by friction, sufficient heat to prevent the accumulation of ice and snow on these brake parts during winter time. In addition, brake unit designs with "zero" clearance are simple in construction and accordingly offer the advantage of relatively low cost construction. Due to the many brake units employed on a train, however, this so-called "zero" clearance arrangement requires a considerable expenditure of train power during brake release, in order to overcome the continuous drag of the brake shoes. With today's high cost of fuel, any cost savings realized during manufacture is more than absorbed by the cost of the extra fuel consumed.